The goal of this proposed research is to define the expression and function of the ecto-nucleotidase NTPDase2 in the liver. This project will extend the findings of the intial K08 application into a novel area for the PI, which should ultimately lead to an ongoing stream of research in this area. The aims of the initial K08 application were to define the P2Y receptor subtypes expressed in bile duct epithelia (BDE), to define the polarized expression of these receptors in BDE, and to determine whether these receptors link to bile ductular secretion. As hypothesized, BDE were found to express multiple P2Y subtypes, to express these subtypes at both basolateral and apical plasma membrane domains, and to link to bile ductular secretion. However, an unexpected finding was the selective inactivation of basolateral P2Y receptors by nucleotide hydrolysis. To investigate this finding further, the expression of ecto-nucleotidases known as nucleoside triphosphate diphosphohydrolases (NTPDases) in the liver was investigated. The ectonucleotidase NTPDase2 was found to be expressed in portal fibroblasts (PF) surrounding intrahepatic bile ducts, which provides a likely explanation for the selective hydrolysis of nucleotides at the basolateral aspect of BDE. New data suggest that NTPDase2 functions to regulate the proliferation of BDE through inhibition of basolateral bile ductular P2Y receptors. We now propose to investigate the physiologic function of NTPDase2 in the liver through the three following Specific Aims: (1) Determine whether PF suppress the proliferation of bile duct epithelia (2) Determine whether blockade of NTPDase2 expression in PF via NTPDase2 siRNA restores proliferation of bile duct epithelia (3) Determine whether blockade of NTPDase2 expression in PF via common bile duct ligation restores proliferation of bile duct epithelia. The experiments proposed in these specific aims will provide the basis of several new lines of liver disease research and should provide novel therapeutic targets for treatment of cholestatic and fibrotic liver disease.